The present invention relates to a power supply circuit and a circuit substrate, particularly to a circuit for supplying alternating-current power to a Josephson device, and to a circuit substrate which incorporates the a.c. power supply circuit, and which serves as a mount for a Josephson device.
Josephson devices, which effect ultra-high speed operation under superconductivity at very low temperatures, are immersed into a container of a coolant such as liquid helium. An alternating-current power supply circuit is provided for connecting the Josephson devices with an external a.c. source, located outside of the container.
Since there are a number of gates in the Josephson device, a larger supply current is required even though the gates individually consume less power. The diameter of an external feed cable must therefore be of sufficient magnitude to carry the larger current; however sealing problems can arise due to endothermic breakdown at the bond between the cable and the container, impairing airtightness therein. To overcome this, a feed cable having a smaller diameter can be employed, wherein power is supplied at higher voltage and lower current. Meanwhile, the Josephson device requires the larger current, such that it becomes necessary to convert the power into a lower voltage and a higher current.
Japanese Patent Gazette Publication No. 30208/1990 discloses an alternating-current power supply circuit including a superconducting thin film inductor, and a capacitor having electrodes formed of superconducting material, wherein the power is converted into a lower voltage and a higher current by resonant lines.
Therein, the a.c. power supply circuit must necessarily be manufactured of superconducting materials. Accordingly, wherein the power supply circuit is manufactured with the Josephson device-mounting circuit substrate, fabricated from an insulative substrate material, it must be formed onto the substrate by thin-film coating technique. The a.c. power supply circuit will consequently occupy a larger area on the substrate, requiring that the substrate itself be of corresponding size. Moreover, manufacture of the circuit substrate is quite difficult, owing to the complex structure of the superconducting-material formed a.c. power supply circuit.